Story highlights

As nervous residents go about their day, police continue to execute raids, other operations

Belgian Prime Minister says his country needs to "improve" in its fight against terrorism

Some metro trains are passing through -- but not stopping -- at station where one bombing took place

Brussels, Belgium (CNN)Explosions and gunfire Friday exacerbated the uneasy mood of Belgium's capital, a city that has become the focal point in Europe's fight against terrorism following the bloody attacks here just days ago.

Residents of Brussels anxiously moved on with their lives as more police raids followed the vicious attacks in which more than 30 people were killed Tuesday.

Police operations seem commonplace now, with several taking place Friday. One was in the district of Schaerbeek, near where a taxi driver picked up three conspirators and took them to Brussels Airport before the bombings.

Witnesses told CNN that during the police activity Friday they heard two explosions, while others reported gunfire near a subway station.

One man said that his son, who has a shop inside a now closed-off area, saw an armed individual who emerged from a metro shop get shot in the leg by police.

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The operation ended with the arrest of one person linked to Tuesday's attacks, Schaerbeek Mayor Bernard Clerfayt told public broadcaster RTBF.

The mayor said that arrested person was wounded. It was not clear if that individual was the same one the shopkeeper saw shot in the leg.

It's hard to escape the tension in Brussels where soldiers line the streets near the central subway station, their hands gripping guns.

Photos:World reacts to Brussels bombings

Photos:World reacts to Brussels bombings

Airport workers and their relatives in Brussels, Belgium, hold a candlelight vigil Wednesday, March 23, to pay tribute to those who were killed in terrorist attacks the day before. On Tuesday, explosions rocked the city's airport and a subway station.

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Belgian national flags are projected onto the National Gallery in London's Trafalgar Square on March 23.

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A woman in Brussels pauses after people observed a minute of silence at the Place de la Bourse on March 23.

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Teresa Mancheno, a maintenance worker at Newark Liberty International Airport, attends a vigil in Newark, New Jersey, on March 23.

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European Union flags fly at half-staff outside the European Commission in Brussels on March 23.

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A young girl lights a candle at the Place de la Bourse in Brussels on Tuesday, March 22.

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An image of the Belgian flag is displayed on the Trevi Fountain in Rome on March 22.

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The Eiffel Tower is lit up with the colors of the Belgian flag on March 22.

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Servicemen with Azov, a Ukrainian volunteer battalion, hold torches during a tribute ceremony at the Belgian Embassy in Kiev, Ukraine, on March 22.

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U.S. President Barack Obama and his family observe a moment of silence as they attend a baseball game in Havana, Cuba, with Cuban President Raul Castro, right, on March 22.

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A woman reads messages written on the ground at Brussels' Place de la Bourse on March 22.

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A New York City church holds Mass for victims of the Brussels attacks on March 22.

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A man places flowers outside the Belgian Embassy in Moscow on March 22.

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A man looks at flowers and messages outside the stock exchange in Brussels on March 22.

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Democratic presidential candidate Hillary Clinton, center, stands for a moment of silence during a roundtable with tribal leaders in Puyallup, Washington, on March 22.

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A woman leaves a bouquet of flowers at the base of the Belgium and European Union flags, which were flying at half-staff March 22 at the Belgian Embassy in Washington.

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Activists in Multan, Pakistan, condemn the Brussels attack on March 22.

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A woman lays flowers at the steps of the Belgian Embassy in Berlin on March 22.

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A boy at a makeshift migrant camp shows support for the victims near the village of Idomeni, Greece, on March 22.

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Mayors of Istanbul districts walk with consuls from various countries, including Belgium, during a protest condemning terrorism on March 22.

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People in Turin, Italy, take part in a rally to remember the victims on March 22.

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France's Parliament observes a minute of silence on March 22.

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Members of Quebec's National Assembly have a moment of silence on March 22.

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"We all know that we are not safe anywhere," one woman said. "It can happen anywhere and at any moment."

The effects are felt in many ways, including in neighborhoods swarmed by police and near the attack sites. Brussels Airport, for instance, won't have passenger flights until Sunday at the earliest.

More metro stations are open -- about half of the nearly 80 stops -- but they still close at 7 p.m. instead of the usual 1 a.m. Some trains are running through the Maelbeek station, though it is closed. Workers overnight Thursday installed screens and plastic to cover up the bomb damage from the view of passing trains.

A Belgian man said the whole atmosphere in the city has "the feeling of war." That may be true, but others welcome the added security.

"It makes me safe," one woman said. "A lot safer."

At the Maelbeek train station a white, large wreath had been left by the Pompes Funebres Islamiques (Islamic Funeral company). The man who left the flowers said they were leaving others at other sites in Brussels. And even though he declined an interview, he told CNN, "the terrorists were not real Muslims."

Can Europe stop the next attack?

Belgian authorities conducted searches in Schaerbeek for several hours into Friday morning, sealing off streets for several blocks. At one point, masked teams in hazmat gear could be seen exiting a building and heading toward a police van.

Friday's raid came just days after police -- acting on the taxi driver's tip -- raided an apartment in the district and uncovered 15 kilograms of the explosive TATP, chemicals, a suitcase with nails and screws, an ISIS flag and other equipment meant to make explosives, Belgian federal prosecutor Frederic Van Leeuw said.

These kinds of police actions suggest authorities' urgency to catch those responsible for Tuesday's massacres -- and to prevent the next attack.

At least nine people have been arrested in the past day in Europe. Six people were taken into custody overnight in Belgium. Of those, three have since been released.

Meanwhile a man in France suspected of being in an "advance stage" of planning his own attack was also detained. Afterward, law enforcement found 2 kilograms (4.4 pounds) of TATP and a Kalashnikov rifle in a raid in Argenteuil on Paris' outskirts, a source briefed on the investigation said.

There's also a growing feeling that those opposing ISIS can do more. Some of this relates to continuing military efforts in the Middle East. Some has to do with better intelligence and cooperation among allies.

Belgium, especially, has come under fire. Interior Minister Jan Jambon offered to resign after acknowledging missed opportunities to stop one of the suicide bombers, Ibrahim El Bakraoui. And Prime Minister Charles Michel said he talked with Kerry about how "to do better (and) work together to be more efficient."

Michel said, "We need to accept that we need to improve the fight against terrorism in Europe and in Belgium."

A young girl looks out of the window of a bus after airport evacuations.

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Photos:Terror attacks in Brussels

People stand near the airport after evacuations.

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Passengers gather outside the airport.

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Police officers stand guard near the Maelbeek metro station.

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A police helicopter flies above the area near the subway station.

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People embrace outside the Brussels airport.

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People are led away from the airport after the attacks.

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A victim receives first aid near the Maelbeek metro station.

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Ambulances arrive at the airport.

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The terrorist cell behind the Paris and Brussels attacks is being wiped out but France is still being threatened, French President Francois Hollande said to journalists ahead of a meeting with former Israeli President Shimon Peres.

"The Paris attacks last year, Brussels, without forgetting what happened in Copenhagen, they all trace back to the troubles in Middle East, especially the war in Syria and Iraq," he said.

Hollande said that despite arrests, the cell and other networks remain dangerous.

Source: Man detained in Germany had revealing texts

In Giessen, a German town about 70 kilometers (43 miles) north of Frankfurt, police arrested a 28-year-old Moroccan man following a routine police check at a train station, a source briefed by German investigators told CNN.

The man, suspected of being connected to the Brussels attack cell, received a text message three minutes before the Brussels metro attack stating "Fin," the French word for end.

Police sought out the man after they spotted him lingering on the platform with a bag, the source said. When they checked his passport they discovered he had been barred from the Schengen area, which allows for passport-free travel in 26 European countries, because of his involvement in robberies.

Authorities recovered some text messages from his phone. One of them had the name of Khalid El Bakraoui, the Brussels metro bomber. Another was sent to him at 9:08 a.m., three minutes before explosion, and stated simply "Fin."

German investigators do not know who sent the message to him. Police also found a bill on his person from a Belgium hospital dated March 18 for treatment for injuries to his torso. German investigators believe it is possible the man was injured during a raid in Brussels last week, but have not firmly established this, the source said. They found documentation indicating he had recently traveled to Germany from Belgium, the source said.

Ten days ago, Belgian police exchanged fire with gunmen inside an apartment in Brussels. Several of those people inside, including Paris attack suspect Salah Abdeslam, escaped from the residence through the roof. Two, including Abdeslam, subsequently were taken into custody.

A second man arrested Thursday in Dusseldorf was also connected to El Bakraoui and his brother, Ibrahim, according to the source. German investigators have established the man took a flight from Amsterdam with Ibrahim El Bakraoui to Turkey last summer and was also arrested along with El Bakraoui in Gaziantep, near the Syria border.

Both men were deported back to Amsterdam on the same flight, the source told CNN.

Ibrahim and Khalid El Bakraoui were included in a U.S. counterterrorism watch list, a U.S. official familiar with the matter confirmed to CNN. Ibrahim El Bakraoui was on the list before the Paris attacks last November for his suspected ties to terrorism.

Khalid El Bakraoui was added after the Paris attacks because of his alleged involvement in helping to pay for a safe house for some attackers.

Abdeslam was interviewed for two hours by Belgian authorities on Saturday, Van Leeuw, Belgium's federal prosecutor, said. Abdeslam has refused to answer questions in subsequent interviews, the prosecutor said.

Authorities have said Ibrahim El Bakraoui and ISIS bomb-maker Najim Laachraoui were killed in the blasts at the airport, and Khalid El Bakraoui on a train near the Maelbeek metro station.

Authorities are looking for two other men. One appears in surveillance footage holding a large bag at a Brussels metro station, according to Belgian public broadcaster RTBF. It is possible that he, like Khalid El Bakraoui, didn't survive the subway blast.

The other is in another surveillance image wearing a hat and light-colored clothing alongside Laachraoui and Ibrahim El Bakraoui, with all three men rolling luggage carts through Brussels Airport.